I see this argument a lot. Frankly I've thought of it at times too. Now that I see that info marketing makes gobs of money I understand better why people do it.
I remember listening to Ron LeGrand who stated he made a lot of money in Real Estate, but made a lot more marketing the "How to" stuff. Armando Montelongo is headed down the same path.
Buyers of info products are not stupid. They know that the author is making money on them. What seems to ring "untrue" are statements like " I'm doing this because I love people and want to share" - even if that might really be the case. When I hear that I think " Then give it to me free if you want to help so much "
Some marketers get successful in an area specifically so they can sell info products about it. I'm told John Childers did that. He became successful in Real Estate so he could sell info on how to be successful in real estate.
What is your retort to the question:
If you made so much money doing X , why are you selling me this info product?